1. Field of the Invention
The present invention relates to a construction machine such as a hydraulic shovel, and more particularly to a frame constitution of a lower traveling body in a construction machine.
2. Description of the Related Art
As shown in the side view of FIG. 8, a conventional hydraulic shovel 11 comprises a lower traveling body 12 to enable movement, and an upper slewing body 13 which is mounted slewably onto the lower traveling body 12.
In the lower traveling body 12, a drive shaft 15 and a pivot 16 are attached respectively to the two end portions of a truck frame 14, and a crawler belt 17i is wrapped around the drive shaft 15 and pivot 16.
The hydraulic shovel 11 is driven by a power source engine, the power of which is converted into oil pressure by a hydraulic pump to drive a traction motor. This causes the drive shaft 15 to rotate, which drives the crawler belt 17 to rotate, and as a result, traveling is performed.
According to Japanese Patent Application 2002-332379, as shown in FIG. 9, in a frame 12F of the lower traveling body, sheet metal covers 21, 22 are welded to the upper face portion and lower face portion of a box-shaped rotary case 20 having an attachment ring 20r to which the upper slewing body 13 is attached slewably, and an inverse C-shaped case 23 formed from sheet metal is fixed to the two end portions thereof by welding. An upper face plate 24 is formed on the sheet metal inverse C-shaped case 23.
The truck frame of an axle-equipped vehicle is disclosed in Japanese Unexamined Patent Application Publication H10-236346.
Since the hydraulic shovel 11 described above performs operations outside, the crawler belt 17 is rotated to travel over various ground conditions, and hence the crawler belt 17 churns up earth, mud, and so on.
As shown in FIG. 8, the sheet metal cover 21 and upper face plate 24 disposed in the vicinity of the crawler belt 17 extend in a horizontal direction, and hence the earth, mud, and so on that is churned up by the crawler belt 17 accumulates on the upper face plates 24, 24.
Consequently, a worker must remove the accumulated earth, mud, and so on, and if the earth, mud, and so on are left to accumulate, they cause running resistance when the hydraulic shovel 11 is operated.
Measures such as opening a hole in the cover 21 may be considered so that the earth falls off the cover 21.
However, the cover 21 and the like invariably have a level part, and it is therefore difficult to solve the problem of earth accumulation.
To improve earth removal, a constitution has been considered in which the frame 12F of the lower traveling body is divided into the central box-shaped rotary case portion and the pair of truck frame portions on the opposite sides, and the truck frames are connected to the rotary case portion via a pair of leg-shaped connecting members.
According to this constitution, the rotary case portion and the truck frame portions are connected via a pair of connecting members, and hence an open space is formed between the pair of connecting members through which the earth that is churned up by the crawler belt 17 passes and falls to the ground. Thus earth removal can be precipitated favorably.
Conventionally, however, the truck frames 14, to which excessive loads may be applied, are connected to the rotary case 20 via the plate-form sheet metal covers 21, 22 which are single plates as shown in FIG. 9. Hence stress generated by a load acting on the truck frames 14 can be transmitted to the single plate covers 21, 22 extending in a planar direction, thus eliminating problems relating to strength.
In the case of the aforementioned constitution, on the other hand, the truck frame portions on which loads act and the central rotary case portion are connected via the connecting members which are constituted separately, and hence, depending on the connection configuration between the connecting members and the central rotary case portion, the vehicle body may break.
Therefore, the connection configuration between the connecting members and the rotary case portion needs to be considered to ensure that stress generated by a load transmitted from the truck frame portions to the connecting members is transferred appropriately from the connecting members to the central rotary case portion.